I wouldn't say we've been doing anything conscious or deliberate or planned enough to be dignified by an acronym- but dh and I have been allowed ourselves to use each other's languages to dcs, both in conversation and when singing/reading aloud. Dcs who are now 11 and 15, speak both languages fluently and happily and do not appear confused. Dd also reads books in Swedish at an age appropriate level (i.e. grown-up) and texts Swedish friends: ds is not much of a reader in any language.
The main reason people are wary of this approach is because of the risk that the majority language takes over and it gets harder and harder to maintain the minority. We reckoned we had a lot of compensatory factors in place: spending summer holidays with Swedish speaking family, a fine collection of Swedish books and DVDs, lots of bedtime stories- but even so we have sometimes had to remind ourselves to speak more Swedish.
When we are in Sweden the whole family speaks Swedish for the duration, when we are at home in the UK we speak whatever we fancy (often switching languages in the course of the conversation), when we are with other English speakers we speak English. Dd and ds do speak Swedish to each other, though not all the time.
Another reason people are put off BPBL is for fear the children will pick up a foreign accent from the non-native speaker. I can't say we've had much of a problem with that: dh's accent is very poor but dcs worked that one out at a young age and have never tried to imitate him; in fact, they stopped him reading aloud in Swedish when they were little (but never objected to my reading aloud in English).
There were times when ds was little when I did worry about his Swedish accent, but then I listened to my Swedish nephews and realised a lot of it was just the common baby errors. I think when you have a bilingual child you tend to blame anything linguistic they do wrong on bilingualism, when in actual fact the child may be further ahead than his monolingual peers.
We also talked a lot to the children about languages, what they were called, how you did things differently in the two languages, how people spoke different languages at different times.
But I would say the absolutely vital thing is getting in enough exposure of the minority language. And getting them to feel positive about it. If you can manage those two, then the actual method is probably not that important.